fix(cron): close abandoned coroutine when asyncio.run() raises RuntimeError

Cherry-picked from PR #2290 by @Mibayy. Closes #2138.

When asyncio.run() raises RuntimeError (running loop exists), the
coroutine was created but never awaited, producing a RuntimeWarning
on GC. Extract coro before try, call coro.close() in the except
branch before falling back to ThreadPoolExecutor.

cron/scheduler.py

@@ -170,11 +170,15 @@ def _deliver_result(job: dict, content: str) -> None:
     )
 
     # Run the async send in a fresh event loop (safe from any thread)
+    coro = _send_to_platform(platform, pconfig, chat_id, wrapped, thread_id=thread_id)
     try:
-        result = asyncio.run(_send_to_platform(platform, pconfig, chat_id, wrapped, thread_id=thread_id))
+        result = asyncio.run(coro)
     except RuntimeError:
-        # asyncio.run() fails if there's already a running loop in this thread;
+        # asyncio.run() checks for a running loop before awaiting the coroutine;
-        # spin up a new thread to avoid that.
+        # when it raises, the original coro was never started — close it to
+        # prevent "coroutine was never awaited" RuntimeWarning, then retry in a
+        # fresh thread that has no running loop.
+        coro.close()
         import concurrent.futures
         with concurrent.futures.ThreadPoolExecutor(max_workers=1) as pool:
             future = pool.submit(asyncio.run, _send_to_platform(platform, pconfig, chat_id, wrapped, thread_id=thread_id))